The somber event featured speeches attesting to the bravery of those who were caught in the Twin Towers that morning more than 13 years ago, along with the bravery of those who ran into them after the planes struck.

During President Obama’s remarks, he recalled the story of the man in the red bandanna who came to the aid of a group of people trapped on the burning 78th floor of the South Tower:

It seemed as if there was no way out. They didn't know his name, they didn't know where he came from but they knew their lives had been saved by the man in the red bandanna. … He had a big laugh and a joy of life and dreams of seeing the world. He worked in finance, but he had also been a volunteer firefighter. And after the planes hit, he put on that bandanna and spent his final moments saving others.

The man went unidentified for months, until his mother recognized his description. His name was Welles Crowther, 24. His mother, Alison, attended the ceremony, along with Ling Young, a woman he saved. One of his red bandannas is now on display at the museum. “All those who come here," said Obama, "will have a chance to know the sacrifice of a young man who, like so many, gave his life so others might live.”

Also attending the ceremony and taking a tour of the museum were former New York mayors Rudy Giuliani and Michael Bloomberg, as well as the current mayor, Bill DeBlasio; Bill and Hillary Clinton; the governors of New York and New Jersey, Andrew Cuomo and Chris Christie, and many more.

The event featured a performance of 'Amazing Grace' by LaChanze, whose husband died in the attacks. The museum will open to the public on May 21; until then, it is available to victims' families and first responders.